So I have a like new SUM Olympic Arms barrel. problem is I can't get a bolt to close on a 223 go gauge. The barrel is marked 5.56, but that shouldn't matter right? Can I find an inexpensive fix or do I have a paper weight?

Have a reamer? You could stick one in and give it a twist until the bolt closes. Trying to find a different bolt is probably going to be like finding a needle in a haystack.

Or just size your ammo to fit.

SUM= stainless ultra match-- basically a match barrel.

The SUM barrels were not chambered in 5.56 nato to my limited knowledge of them. They were chambered in 223 saami, which is a little different than 5.56x45.

Try a 223 go gauge and it should close on it.

Thanks Tyrone. my thoughts too.

The 5.56 chamber should be just a wee bit more generous in measurements than a 223. The 223 go gauge should still allow the bolt to close, with the extractor and ejector in place. To properly headspace you should remove the extractor and the ejector from the bolt and cut the chamber until the bolt closes on the go guage but not on the no go. Then re-install the extractor and ejector.

If it is a nitrided barrel, it will eat up a high speed steel reamer. So a carbide reamer would be best used to start with. When cutting a chamber, best to always use a lathe at low speed with cutting oil and clean frequently.

john, you are right on SUM but it is marked 5.56-1/8.5 twist? we tried the 223 go gauge and would not close. however I just tried what Tyrone suggest and carefully put a sized case in a spare bolt+ carrier and the bolt locked in?

See my post in "Gunsmithing" section. I had exactly the same problem. I have two Olympic barrels and they both shoot great.

cant you send it back? what id try first is loading a couple rounds using a small base die and see if the bolt closes on them. if you dont handload try the factory ammo you have. if it chambers and ejects easily by hand why worry about iy

Send it back to who? Olympic?

Olympic closed after more than 30 years in business back around 2018/19'ish.

The problem is its olympic... they tried. They were just not capable for the most part.

rost. I respect your opinion since I know you know your way around ARs. but The SUM barrel was thought to be an extremely accurate one. this one apparently was cut a tad short so at least its salvageable. as a 5.56 barrel, I want to be able to shoot both 5.56 and 223. so find a guy with a reamer or buy one myself.

They were really accurate barrels. They just had no clue how to set them up correctly unfortunately.

i didnt know they quit but i thought i heard back around then that remington owned them. i had to junk olys back in the day. worse ars i ever owned. but i bought their cheap sportical back must have been close to the time they went under and that thing was a tack driver. told my buddy and he bought one and said the same about his. wish i would have kept it. it was the lightest 16 in gun ive owned and that made it handy rifle

Not an uncommon experience...